There are many types of marine instruments available for commercial and pleasure craft today. Some of them include devices for measuring water depth, boat speed, temperature, as well as, locating fish. The present invention resides in a sonar device, and particularly the type called a search-light sonar. A sonar is an echo sounder which includes a transducer to emit a soundbeam downwardly from the boat. When the beam strikes something, such as the bottom, it will reflect an echo back to the transducer. This is converted to electrical energy, amplified and displayed as information on a screen. It may also display information on a paper graph, flashing device and even on video displays.
While echo sounders initially were employed to give information about depth, more sophisticated types of devices provide information about the location of fish, both individuals and schools, as well as, to the type of bottom that is located directly below and outwardly around the boat.
A searchlight sonar employs a narrow soundbeam that can be pointed in a variety of directions. Generally speaking, the beam is directed in a forward and downward direction. For example, it may be projected downwardly from the boat at 45.degree. while simultaneously oscillated back and forth over an arc which typically might be 90.degree.. It is to this type of mechanism that the present invention has particular applicability.
Searchlight or scanning sonars are not new even in fish locating. Basically, a scanning sonar employs a transducer which is tiltable about a substantially horizontal axis so as to be located with a desired amount of downwardly inclined tilt. It is also rotatable about a horizontal axis so as to be able to scan back and forth, left and right, while the boat proceeds forward at a slow speed. Traditionally, the transducers have been mounted in yokes which are rotated by one motor and which are tilted by a second motor, which is mounted either on the yoke or the yoke support. Thus, one of the motors has to accommodate the mass of the transducer plus another motor as well.
The yokes are frequently mounted on turntables and the turntable itself carries the second motor for tilting the transducer. This involves a substantial amount of mass for the first motor to rotate.
Accordingly, it is an object of this invention to produce a searchlight sonar having the smallest mass possible in order to be driven by the smallest motors possible in order to reduce size, weight and cost.
Another problem encountered in prior art searchlight sonars is that the wiring required by two motors, one of which must move the other motor, is complicated and subjects its soldering to undesirable stress.
Thus, yet another object of this invention is to reduce wiring to a minimum and assure that the stress that it is subjected to is minimized.
In a fish scanning operation the sonar is adjusted to a predetermined downward tilt and this tilt must be maintained as the sonar transducer is panned or otherwise oscillated to maintain a constant angle of scanning. If the tilt angle were constantly varied as the scanning angle changes, the resultant readout, be it on a paper graph or on a visible display, would be compounded and to a large degree unintelligible.
Consequently, another feature of this invention is to produce a scanning sonar with means to assure that the sonar transducer is maintained at the specific tilt angle to which it is initially set.